The D$-$string on a properly tuned guitar produces a tone with a fundamental frequency of $146\mathrm{.}8$ Hz$.$ The oscillating length of a D$-$string on a certain guitar is$0\mathrm{.}66$m$.$Part $($a$)$What is the wavelength, in meters, of the standing wave in the D$-$string when it is oscillating at its third harmonic $($also called its second overtone$)?$Part $($b$)$ Determine the frequency, in hertz, of the third harmonic of the tone produced by the properly tuned D$-$string.$$Part $($c$)$ The guitarist shortens the oscillating length of the properly tuned D$-$string by$0\mathrm{.}14$m by pressing on the string with a finger. What is the fundamental frequency, in hertz, of the new tone that is produced when the string is plucked?$$